You can color both text and its background.
The commands for this can be found on the ribbon tab Home | group Character.
Font color: Via the icon of the command group "Paragraph"
For the Font color 
, proceed as follows:
| 1. | Select the desired cells or text, and click on the small arrow to the right of the icon (thus, not on the icon itself). |
| 2. | Select the desired color from the dropdown menu. |
| Tip: To format more text in the same color, select the text and then click on the icon itself because the last color used will be applied again. |
The Font color can be found both as a direct button in the command group and in the dialog box. The Background color, however, can only be changed via the dialog box (see below).
Background color: In the dialog box of the command group "Character"
Insofar as only the font color is concerned, the selection in the dialog box corresponds exactly to the button described above. However, in addition to the font color, you can also change the background color in the dialog box.
Proceed as follows:
| 1. | Select the desired cells or text. |
| 2. | Click on the group arrow in the bottom right corner of the ribbon tab Home | group Character. In the dialog box, switch to the Font tab. |
| 3. | Open the dropdown list Background color and select a different color instead of the default Transparent. |
The text is highlighted with this color.
Tip: If you change the background color in this manner, it will only affect the individual characters within the cell. If you want to color the entire cell, however, you should use the ribbon command Home | group Format | Shading instead.
Notes
Color lists only offer a few standard colors, but you can always compose your own colors. To do so, click on the entry Define color... at the end of the dropdown list. (For more information, see also Document properties, Colors tab.)